1. Field of the Invention
The present invention relates to an inertial separator for separating foreign particles from an airflow, particularly to particle separation in inlet airflow to gas turbine engines.
2. Description of the Prior Art
The injection of foreign particles into the inlet of a gas turbine engine can cause serious damage to the components of the engine. For example, military helicopters are subject to numerous take-offs and landings from untreated areas where they may be exposed to large amounts of sand and dust. The injection of the sand and dust will cause erosion of the engine components, thus reducing the engine's life expectancy.
Helicopters located on off-shore drilling platforms are subject to large quantities of salt spray which can result in corrosion of the engine components and thus cause serious engine damage. The problem arising from injection of birds into the gas turbine engine while an aircraft is in flight has always been a concern.
Solutions to the problem have been suggested with varying degrees of success. It is well known, for instance, from U.S. Pat. No. 3,766,719, issued Oct. 23, 1973, to United Aircraft Corporation, naming William J. McAnally III as inventor, that the inlet airflow can be conducted axially through an annular passageway upstream of the engine inlet, the annular passageway being contoured such that the airflow containing the particles to be separated is first deflected in a divergent manner and the passageway is abruptly turned so that it converges towards the central axis. A splitter in the form of an annular ring is provided in the converging passageway which is concentric to the axis of the inlet and divides the passageway between a bypass passage between the outer shroud and the splitter. The core airflow will pass between the splitter ring and the center by an inner wall.
As sand or other particles are injected in the inlet, the inertia of the heavier particles will cause those particles which clear the deflecting inner wall of the inlet to pass directly into the bypass area. Other particles which strike the deflecting inner wall surface will be deflected against the shroud or outer wall and hopefully bounce into the bypass area over the splitter. The same applies to moisture and salt particles.
The separator system just described, with particular reference to U.S. Pat. No. 3,766,719, is also illustrated in U.S. Pat. No. 3,148,043, Richardson et al, Sept. 8, 1964, and in a recent U.S. Pat. No. 4,389,227, issued June 21, 1983, to John R. Hobbs. One of the problems which still remain, however, is that the particles which are deflected by the surface of the inner or deflecting wall in the intake, bounce back off the outer wall randomly, depending on what portion of the deflecting wall they may have struck and at what angle they may have struck the deflecting wall. These random bouncing particles may bounce back into the core airflow upstream of the splitter ring. If they bounce onto the splitter ring, such particles are thus separated and passed into the bypass area. However, those particles which bounce into the core airflow will of course be entrained into the engine.
Furthermore, it has been found that pressure losses are increased where the aerodynamic stagnation point does not occur right on the leading edge of the splitter ring. If the aerodynamic stagnation point occurs downstream of the splitter ring leading edge on top of the splitter and since the core airflow reverses and follows a sharp turn of the splitter ring, undergoing rapid acceleration, followed by abrupt deceleration, stalling may occur along the underside of the splitter ring as it enters the core passageway.